The present invention relates to tissue stimulation systems and more particularly to evaluating stimulation therapies and patient satisfaction with stimulation therapies.
One example of a stimulation system is a spinal cord stimulation system (“SCS”). Spinal cord stimulation is a well accepted clinical method for reducing pain in certain populations of patients. An SCS system typically includes an Implantable Pulse Generator (IPG) or a radio-frequency (RF) transmitter and receiver, electrodes, electrode leads, and when necessary, lead extensions. The electrodes are implanted along the dura of the spinal cord, and the IPG or RF transmitter generates electrical pulses that are delivered, through the electrodes, to the dorsal column and dorsal root fibers within the spinal cord. Individual electrode contacts (the “electrodes”) are arranged in a desired pattern and spacing in order to create an electrode array. Individual wires within one or more electrode leads connect with each electrode in the array. The electrode leads exit the spinal column and attach to one or more electrode lead extensions, when necessary. The electrode leads or extensions are typically tunneled around the torso of the patient to a subcutaneous pocket where the IPG or RF-receiver is implanted.
Spinal cord stimulators and other stimulation systems are known in the art. For example, an implantable electronic stimulator is disclosed in U.S. Pat. No. 3,646,940 issued Mar. 7, 1972 for “Implantable Electronic Stimulator Electrode and Method” that provides timed sequenced electrical impulses to a plurality of electrodes. As another example, U.S. Pat. No. 3,724,467 issued Apr. 3, 1973 for “Electrode Implant For The Neuro-Stimulation of the Spinal Cord,” teaches an electrode implant for the neuro-stimulation of the spinal cord. A relatively thin and flexible strip of physiologically inert plastic is provided as a carrier on which a plurality of electrodes are formed. The electrodes are connected by leads to an RF receiver, which is also implanted.
In U.S. Pat. No. 3,822,708, issued Jul. 9, 1974 for “Electrical Spinal Cord Stimulating Device and Method for Management of Pain,” another type of electrical spinal cord stimulation device is taught. The device disclosed in the '708 patent has five aligned electrodes, which are positioned longitudinally on the spinal cord. Electrical pulses applied to the electrodes block perceived intractable pain, while allowing passage of other sensations. A patient operated switch allows the patient to adjust the stimulation parameters.
An SCS system treats chronic pain by providing electrical stimulation pulses through the electrodes of an electrode array located at the distal end of a lead placed epidurally next to a patient's spinal cord. The combination of electrodes used to deliver stimulation pulses to the targeted tissue constitutes an electrode configuration. In other words, an electrode configuration represents the polarity, being positive, negative, or zero, and for certain SCS systems with such capabilities, relative percentage of the current or voltage provided through each of the electrodes. Electrode arrays used with known SCS systems may employ between 1 and 16 electrodes on a lead. Electrodes are selectively programmed to act as anodes, cathodes, or left off, creating an electrode configuration. The number of electrodes available, combined with the ability to generate a variety of complex stimulation pulses, presents a huge selection of electrode configurations and stimulation parameters (together referred to herein as “stimulation sets”) to the clinician. When an SCS system is implanted, a procedure is performed to select one or more effective stimulation sets for a particular patient. Such a session of applying various stimulation parameters and electrode configurations may be referred to as a “fitting” or “programming” session. Additionally, a series of electrode configurations to be applied to a patient may be organized in a steering table or in another suitable manner.
Other parameters that may be controlled or varied in SCS are the frequency of pulses provided through the electrode array, pulse width, and the strength (amplitude) of pulses delivered. Amplitude may be measured in milliamps, volts, etc., as appropriate, depending on whether the system provides stimulation from current sources or voltage sources. With some SCS systems, the distribution of the current/voltage across the electrodes (including the case of the pulse generator or receiver, which may act as an electrode) may be varied such that the current is supplied via numerous different electrode configurations. In different configurations, different combinations of electrodes may provide current (or voltage) in different relative percentages of positive and negative current (or voltage). Moreover, there may be some electrodes that remain inactive for certain electrode configurations, meaning that no current is applied through the inactive electrode.
Therefore, an “electrode configuration” refers to a polarity and/or to a relative distribution of current or relative magnitude of voltage applied through the electrodes of the electrode array. Electrodes may be positive, negative, or turned off, such that a subset of anodes and cathodes are created within the electrode array. A polarity of each electrode may be a positive or negative “1” or a fraction thereof. For example, one electrode of the electrode array may have a polarity of negative “1” (cathode), while another electrode may have a polarity of positive “1” (anode).
Alternatively, a polarity may be spread out among different electrodes, for example, such that one electrode has a polarity of +0.75, while the other electrode(s) have +0.25. This distribution is known as polarity “distribution” or “percentage” among the electrodes of an electrode array. In the above examples, if an electrode has a polarity of negative 1, it is a cathode with 100% of the negative polarity distribution. If an electrode has a polarity of +0.75, it is an anode with 75% of the polarity distribution (with one or more additional electrodes accounting for the remaining 25% of the positive polarity distribution). Thus, a numerical value may be easily associated with a polarity distribution. In the case of current-controlled electrodes, in this example 75% of the anodic current would emanate from the first anode and 25% of the anodic current from the remaining anode(s). In the case of voltage-controlled electrodes, in this example the voltage magnitude of the first anode (e.g. +3.0 volts or 75%) would be three times that of the other anode(s) (+1.0 volts or 25%). The electrode configuration, along with pulse frequency, pulse width, and pulse amplitude of the voltage/current applied to the selected electrodes may be referred to as a stimulation set.
In order to test the effectiveness on a particular patient of various stimulation parameters and electrode configurations (i.e., parameters sets), it is necessary to provide a series of stimulation parameters in a systematic method. Several such systems exist including the systems disclosed in U.S. Pat. No. 6,393,325, incorporated herein by reference in its entirety, wherein a patient may direct the movement of the stimulus current through a suitable interface. Another method of testing the effectiveness of various stimulation parameters is disclosed in U.S. application Ser. No. 11/026,859, incorporated herein by reference in its entirety. In this Application, during a fitting session with a patient, a clinician uses navigation with two parameter tables to step through and optimize stimulation parameters.
In tissue stimulation applications, various stimulation sets may change the character and success of the patient's experience with the therapy. It would be useful to the clinician to be able to quickly determine the patient's satisfaction with a particular stimulation set for both clinical tracking as well as future programming and adjustment to the stimulation therapy. In previous tissue stimulation systems, patients may have been asked to evaluate the effectiveness of the various stimulation sets that are applied. While the clinician may have sought patient feedback in past systems, a system of evaluating stimulation sets, including evaluations that are not based on memory but are based on more quantitative data, scoring stimulation sets and organizing patient satisfaction is needed.
What is needed is method of creating a patient database including tested stimulation sets and associated feedback on these stimulation sets. Once created, this database may be used in future stimulation sessions, in order to provide the most effective stimulation sets to the patient to meet therapeutic objectives. Additionally, there is a need for evaluating the stimulation set based on patient feedback and/or on frequency of use. Additionally, there is a need for a way to evaluate patient-experienced pain both before and after stimulation pulses are applied to the patient. The associated pain level should be stored in the database in addition to the other patient feedback on the tested stimulation sets.